Electrostatic chuck

ABSTRACT

An electrostatic chuck includes: a ceramic dielectric substrate having a first major surface, a second major surface, and a through-hole; a metallic base plate which has a gas introduction path that communicates with the through-hole; and a bonding layer which is provided between the ceramic dielectric substrate and the base plate and includes a resin material. The bonding layer has a space which is provided between an opening of the through-hole in the second major surface and the gas introduction path and is larger than the opening in a horizontal direction, and a first area in which an end face of the bonding layer on a side of the space intersects with the second major surface being recessed from the opening further than a second area of the end face which is different from the first area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/663,526, filed Mar. 20, 2015, which is based upon and claims thebenefit of priorities from Japanese Patent Application No. 2014-066667,filed on Mar. 27, 2014 and Japanese Patent Application No. 2014-262592,filed on Dec. 25, 2014. The entire contents of these prior applicationsare incorporated herein by reference.

FIELD

Embodiments of the invention relate generally to an electrostatic chuck.

BACKGROUND

In a substrate treatment apparatus for performing etching, chemicalvapor deposition (CVD), sputtering, ion implantation, ashing, exposure,inspection, or the like, as means for adsorbing and holding an object tobe adsorbed (a treatment object) such as a semiconductor wafer or aglass substrate, an electrostatic chuck is used.

The electrostatic chuck is fabricated by inserting an electrode in aceramic dielectric substrate such as alumina and performing firing. Theelectrostatic chuck is for applying power for electrostatic adsorptionto the built-in electrode, thereby adsorbing a substrate such as asilicon wafer by an electrostatic force.

In such a substrate treatment apparatus, for higher throughput, anincrease in output of a plasma process and an increase in temperature ofthe plasma process are progressing. For the higher throughput, a coolingfunction of the object to be adsorbed is one of the main points.Further, realizing the higher throughput leads to an increase in theamount of heat which is input to the substrate treatment apparatus. Forthis reason, a material of a member which can be used in theelectrostatic chuck is limited to a highly thermally-resistant material.

For example, for an adhesive to bond a ceramic dielectric substrate to ametal plate which supports the ceramic dielectric substrate, bondingstrength between ceramic and metal at a high temperature, heattransference from the ceramic to the metal, flexibility capable ofcoping with shear stress due to a difference in thermal expansion,electrical insulation properties, and the like are required. While thereis an adhesive having relatively high thermal conductivity or anadhesive having relatively excellent heat resistance and plasmaresistance, as compared to ceramic, metal, or the like, the plasmaresistance of the adhesive in the plasma process is the lowest amongmembers which are used for the electrostatic chuck. For this reason, thelife of the adhesive becomes the life of the electrostatic chuck.

If the adhesive is damaged in a process such as etching, a ceramicfiller component which improves heat conduction or an elastomercomponent which cannot be gasified sometimes becomes a particle source.Further, if the adhesive is damaged, the thermal conductivity of theadhesive is reduced, and thus a function of heat conduction and afunction of uniformly maintaining the temperature of the object to beadsorbed are not sometimes fulfilled. Therefore, an electrostatic chuckis desired in which it is possible to reduce damage to which theadhesive is subjected.

SUMMARY

According to an aspect of the invention, there is provided anelectrostatic chuck including: a ceramic dielectric substrate having afirst major surface on which an object to be adsorbed is placed, asecond major surface on an opposite side to the first major surface, anda through-hole provided over from the second major surface to the firstmajor surface; a metallic base plate which supports the ceramicdielectric substrate and has a gas introduction path that communicateswith the through-hole; and a bonding layer which is provided between theceramic dielectric substrate and the base plate and includes a resinmaterial, the bonding layer having a space which is provided between anopening of the through-hole in the second major surface and the gasintroduction path and is larger than the opening in a horizontaldirection, and a first area in which an end face of the bonding layer ona side of the space intersects with the second major surface beingrecessed from the opening further than another second area of the endface which is different from the first area.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating theconfiguration of an electrostatic chuck according to the embodiment;

FIGS. 2A and 2B are schematic enlarged views showing the vicinity of abonding layer of the embodiment;

FIG. 3 is a schematic enlarged cross-sectional view of a variation of aportion A shown in FIG. 1;

FIGS. 4A and 4B are graphs illustrating the relationship between adistance d and a temperature difference, and a graph illustrating therelationship between the distance d and conductance;

FIG. 5 is a schematic enlarged view showing the vicinity of anotherbonding layer of the embodiment;

FIG. 6 is a schematic enlarged view showing the vicinity of stillanother bonding layer of the embodiment;

FIG. 7 is a schematic enlarged view showing the vicinity of stillanother bonding layer of the embodiment;

FIG. 8 is a schematic enlarged view showing the vicinity of stillanother bonding layer of the embodiment;

FIG. 9 is a schematic enlarged view showing the vicinity of stillanother bonding layer of the embodiment;

FIG. 10 is a schematic enlarged view showing the vicinity of stillanother bonding layer of the embodiment;

FIG. 11 is a schematic enlarged view showing the vicinity of stillanother bonding layer of the embodiment;

FIG. 12 is a schematic cross-sectional view showing the conditions ofthe simulation;

FIGS. 13A to 13C are schematic perspective views illustrating an exampleof the results of the simulation; and

FIGS. 14A and 14B are schematic perspective views illustrating anexample of the results of the simulation.

DETAILED DESCRIPTION

According to a first invention, there is provided an electrostatic chuckincluding: a ceramic dielectric substrate having a first major surfaceon which an object to be adsorbed is placed, a second major surface onan opposite side to the first major surface, and a through-hole providedover from the second major surface to the first major surface; ametallic base plate which supports the ceramic dielectric substrate andhas a gas introduction path that communicates with the through-hole; anda bonding layer which is provided between the ceramic dielectricsubstrate and the base plate and includes a resin material, the bondinglayer having a space which is provided between an opening of thethrough-hole in the second major surface and the gas introduction pathand is larger than the opening in a horizontal direction, and a firstarea in which an end face of the bonding layer on a side of the spaceintersects with the second major surface being recessed from the openingfurther than another second area of the end face which is different fromthe first area.

According to the electrostatic chuck, regardless of the durability of anadhesive itself, it is possible to reduce damage to which the bondinglayer is subjected. Even if the bonding layer is damaged, it is possibleto reduce the scattering of particles.

According to a second invention, in the electrostatic chuck according tothe first invention, in the first area when viewed in a directionperpendicular to a normal to the second major surface, an angle betweenthe second major surface and the end face becomes larger toward thesecond major surface.

According to the electrostatic chuck, regardless of the durability of anadhesive itself, it is possible to reduce damage to which the bondinglayer is subjected. Even if the bonding layer is damaged, it is possibleto reduce the scattering of particles.

According to a third invention, in the electrostatic chuck according tothe second invention, a third area in which an angle between the secondmajor surface and the end face becomes smaller with distance from thesecond major surface in a direction of the normal is provided.

According to the electrostatic chuck, regardless of the durability of anadhesive itself, it is possible to reduce damage to which the bondinglayer is subjected. Even if the bonding layer is damaged, it is possibleto reduce the scattering of particles.

According to a fourth invention, in the electrostatic chuck according tothe first invention, a distance between the end faces facing each otherbecomes shorter with distance from the second major surface in adirection of the normal.

According to the electrostatic chuck, regardless of the durability of anadhesive itself, it is possible to reduce damage to which the bondinglayer is subjected. Even if the bonding layer is damaged, it is possibleto reduce the scattering of particles.

According to a fifth invention, in the electrostatic chuck according tothe first invention, in a distance d between the end face in the firstarea and a center of the through-hole and a distance D between the endfaces facing each other in the second area, a relational expression of2d≧D is established.

In a case where a cross-sectional structure of the end face isasymmetric, the distance d is set to be a distance of the maximum valueamong the distances between the end face in the first area and thecenter of the through-hole. According to the electrostatic chuck, it ispossible to form a pocket in which particles can be deposited.

According to a sixth invention, in the electrostatic chuck according tothe fifth invention, the distance d is 0.1 millimeters or more and 5.0millimeters or less.

According to the electrostatic chuck, it is possible to attain both areduction in the amount of damage to which an adhesive is subjected anduniform temperature distribution of the object.

According to a seventh invention, in the electrostatic chuck accordingto the first invention, the bonding layer has a bonding portion whichbonds the second major surface and the base plate together, and an endportion which has the end face and forms the space, and a material ofthe bonding portion is different from a material of the end portion.

According to the electrostatic chuck, the end portion is made so as notto contain fillers improving thermal conductivity, and thus it ispossible to reduce occurrence of particles. Further, in a case where asilicone adhesive is used as the bonding portion, a material having moreexcellent plasma resistance than the silicone adhesive can be used forthe end portion.

According to an eighth invention, in the electrostatic chuck accordingto the first invention, the bonding layer has a bonding portion whichbonds the second major surface and the base plate together, and an endportion which has the end face and forms the space, and a material ofthe bonding portion is the same as a material of the end portion.

According to the electrostatic chuck, it is possible to further enhancean adhesive force between the bonding portion and the end portion.

According to a ninth invention, in the electrostatic chuck according tothe seventh invention, thermal conductivity of an adhesive which is usedin the bonding portion is 0.1 watts/meter·kelvin or more, dielectricbreakdown strength of an adhesive which is used in the bonding portionis 1 kilovolt/millimeter or more, and a heat resistance temperature ofan adhesive which is used in the bonding portion is 40° C. or more.

According to the electrostatic chuck, it is possible to use an adhesivewhich can maintain insulation while maintaining good heat transfer evenif the electrostatic chuck is used in a high-temperature process.Further, it is possible to have elasticity capable of alleviating adifference between the thermal expansion of the ceramic dielectricsubstrate and the thermal expansion of the base plate.

According to a tenth invention, in the electrostatic chuck according tothe fifth invention, the electrostatic chuck further includes a porousbody provided in the gas introduction path, wherein in the distance dand a radius R of the porous body, a relational expression of d>R isestablished.

According to the electrostatic chuck, a pocket in which particles can bedeposited is formed, and thus the convection of transfer gas can becreated in the space such that particles are easily deposited in thepocket. That is, the convection of the transfer gas which selectivelydeposits particles in the pocket can be controlled in the space. Forthis reason, even if particles are generated, it is possible to reducethe scattering of the particles. Further, the porous body is provided,whereby it is possible to have high voltage resistance in thethrough-hole and the gas introduction path.

According to an eleventh invention, in the electrostatic chuck accordingto the fifth invention, the distance d is larger than a radius of anopening of the through-hole on a side of the first major surface.

According to the electrostatic chuck, regardless of the durability of anadhesive itself, it is possible to reduce damage to which the bondinglayer is subjected. Even if the bonding layer is damaged, it is possibleto reduce the scattering of particles.

According to a twelfth invention, in the electrostatic chuck accordingto the first invention, a length in the horizontal direction of thespace is longer than a thickness of the bonding layer.

According to the electrostatic chuck, regardless of the durability of anadhesive itself, it is possible to reduce damage to which the bondinglayer is subjected. Even if the bonding layer is damaged, it is possibleto reduce the scattering of particles.

According to a thirteenth invention, in the electrostatic chuckaccording to the seventh invention, the end portion comes into contactwith each of the second major surface and the base plate in a plane, anda length in the horizontal direction of the plane in which the endportion comes into contact with each of the second major surface and thebase plate is longer than a thickness of the bonding layer.

According to the electrostatic chuck, unlike a case where, instead ofthe end portion, an O-ring is provided, the end portion of the bondinglayer can contribute to the bonding between the ceramic dielectricsubstrate and the base plate.

According to a fourteenth invention, in the electrostatic chuckaccording to the thirteenth invention, an outer peripheral portion ofthe end portion, the outer peripheral portion being on an opposite sideto the space when viewed from the end portion, is filled with the resinmaterial.

According to the electrostatic chuck, unlike a case where, instead ofthe end portion, an O-ring is provided, it is possible to preventoccurrence of a space in the bonding layer. The end portion of thebonding layer can contribute to the bonding between the ceramicdielectric substrate and the base plate, and thus, it is possible tomore solidly bond the ceramic dielectric substrate and the base plate toeach other.

According to a fifteenth invention, in the electrostatic chuck accordingto the thirteenth invention, a plane in which the second major surfacecomes into contact with the end portion is on a same plane as a plane inwhich the second major surface is bonded by the bonding layer, and aplane in which the base plate comes into contact with the end portion ison a same plane as a plane in which the base plate is bonded by thebonding layer.

According to the electrostatic chuck, unlike a case where, instead ofthe end portion, an O-ring is provided, the end portion of the bondinglayer can contribute to the bonding between the ceramic dielectricsubstrate and the base plate.

According to a sixteenth invention, in the electrostatic chuck accordingto the thirteenth invention, curvature of the end face in the first areais larger than curvature of the end face in the second area.

According to the electrostatic chuck, unlike a case where, instead ofthe end portion, an O-ring is provided, the end portion of the bondinglayer can contribute to the bonding between the ceramic dielectricsubstrate and the base plate.

According to a seventeenth invention, in the electrostatic chuckaccording to the first invention, the ceramic dielectric substrateincludes a Coulomb material having volume resistivity of 1×10¹⁴ohm·centimeter or more.

According to the electrostatic chuck, regardless of the durability of anadhesive itself, it is possible to reduce damage to which the bondinglayer is subjected. Even if the bonding layer is damaged, it is possibleto reduce the scattering of particles.

Hereinafter, an embodiment of the invention will be described withreference to the drawings. In addition, in each drawing, the sameconstituent elements are denoted by the same reference numerals anddetailed description is appropriately omitted.

In addition, the drawings are schematic or conceptual, and therelationship between a thickness and a width of each portion, the ratiobetween the sizes of portions, and the like are not necessarily the sameas those of reality. Further, even in a case of showing the sameportion, there is also a case where the respective dimensions or ratiosare shown differently according to the drawings.

FIG. 1 is a schematic cross-sectional view illustrating theconfiguration of an electrostatic chuck according to the embodiment.

FIGS. 2A and 2B are schematic enlarged views showing the vicinity of abonding layer of the embodiment.

FIG. 3 is a schematic enlarged cross-sectional view of a variation of aportion A shown in FIG. 1.

FIGS. 4A and 4B are a graph illustrating the relationship between adistance d and a temperature difference, and a graph illustrating therelationship between the distance d and conductance.

In addition, FIGS. 2A and 2B are schematic cross-sectional views in acutting surface passing through the center of a gas introducing path ofa base plate. The following schematic cross-sectional views are those inthe cutting surface.

FIG. 2A is a schematic enlarged view of the portion A shown in FIG. 1.FIG. 2B is a schematic enlarged view of a portion B shown in FIG. 2A.For convenience of description, in FIG. 2A, an electrode 12 is omitted.The omission of the electrode 12 is the same in FIGS. 3, 5, and 6.

FIG. 4A is a graph illustrating the relationship between a distance dbetween an end face 64 in an area A1 shown in FIG. 2A and a center C1 ofa through-hole 15 and the conductance of transfer gas. FIG. 4B is agraph illustrating the relationship between the distance d between theend face 64 in the area A1 shown in FIG. 2A and the center C1 of thethrough-hole 15 and a temperature difference in a plane of an object W.The horizontal axes of the graphs shown in FIGS. 4A and 4B show thedistance d (mm) between the end face 64 in the area A1 and the center C1of the through-hole 15. The vertical axis of the graph shown in FIG. 4Ashows the conductance (sccm: standard cc/min) of the transfer gas. Thevertical axis of the graph shown in FIG. 4B shows the temperaturedifference (° C.) in a plane of the object W.

As shown in FIGS. 1 and 2A, an electrostatic chuck 110 according to theembodiment is provided with a ceramic dielectric substrate 11, a baseplate 50, and a bonding layer 60.

The ceramic dielectric substrate 11 is a flat plate-shaped base materialmade of, for example, sintered ceramic, and has a first major surface 11a on which the object W of adsorption such as a semiconductor substratesuch as a silicon wafer is placed, and a second major surface 11 b onthe side opposite to the first major surface 11 a.

In the ceramic dielectric substrate 11, the electrode 12 is provided.The electrode 12 is interposed between the first major surface 11 a andthe second major surface 11 b of the ceramic dielectric substrate 11.That is, the electrode 12 is formed so as to be inserted into theceramic dielectric substrate 11. The electrostatic chuck 110 generateselectric charge on the first major surface 11 a side of the electrode 12by applying voltage for adsorption holding 80 to the electrode 12 andadsorbs and holds the object W by an electrostatic force.

Here, in the description of the embodiment, a direction (a firstdirection) connecting the first major surface 11 a and the second majorsurface 11 b shall be referred to as a Z-direction, one (a seconddirection) of directions orthogonal to the Z-direction shall be referredto as a Y-direction, and a direction (a third direction) orthogonal tothe Z-direction and the Y-direction shall be referred to as anX-direction.

The electrode 12 is provided in the form of a thin film along the firstmajor surface 11 a and the second major surface 11 b of the ceramicdielectric substrate 11. The electrode 12 is an adsorption electrode foradsorbing and holding the object W. The electrode 12 may be a unipolartype or may also be a bipolar type. The electrode 12 shown in FIG. 1 isa bipolar type, and the two-pole electrode 12 is provided on the sameplane.

At the electrode 12, a connection portion 20 extending to the secondmajor surface 11 b side of the ceramic dielectric substrate 11 isprovided. The connection portion 20 is made by connecting a via (a solidtype), a via hole (a hollow type), or a metal terminal which iselectrically connected to the electrode 12, by an appropriate methodsuch as brazing.

The base plate 50 is a member which supports the ceramic dielectricsubstrate 11. The ceramic dielectric substrate 11 is fixed onto the baseplate 50 through the bonding layer 60 shown in FIG. 2A. That is, thebonding layer 60 is provided between the ceramic dielectric substrate 11and the base plate 50.

The bonding layer 60 has a bonding portion 61 and an end portion 63. Thebonding portion 61 bonds the second major surface 11 b of the ceramicdielectric substrate 11 and the base plate 50 together. The bondinglayer 60 includes a resin material. The bonding layer 60 includes apolymer material which is, for example, a silicone-based, acrylic,modified silicone-based, or epoxy-based polymer material and contains atleast one of carbon (C), hydrogen (H), nitrogen (N), silicon (Si),oxygen (O), and sulfur (S) as its main component. As for the bondingportion 61, for example, a silicone adhesive, a silicone-based heatconduction material having excellent electrical insulation properties,or the like is used. The end portion 63 has, for example, a ring-likeshape. The details of the bonding layer 60 will be described later.

The base plate 50 is divided into an upper portion 50 a and a lowerportion 50 b made of, for example, aluminum, and a communication path 55is provided between the upper portion 50 a and the lower portion 50 b.The communication path 55 is connected, on the one end side, to an inputpath 51 and connected, on the other end side, to an output path 52.

The base plate 50 also plays a role of performing temperature adjustmentof the electrostatic chuck 110. For example, in a case of cooling theelectrostatic chuck 110, a cooling medium flows in from the input path51, passes through the communication path 55, and then flows out fromthe output path 52. In this way, the heat of the base plate 50 isabsorbed by the cooling medium, and thus the electrostatic chuck 110mounted thereon is cooled. On the other hand, in a case of keeping theelectrostatic chuck 110 warm, it is also possible to put a heatmaintaining medium in the communication path 55. Or, it is also possibleto make the electrostatic chuck 110 or the base plate 50 have a built-inheating element. In this manner, if the temperature of the electrostaticchuck 110 is adjusted through the base plate 50, it is possible toadjust the temperature of the object W which is adsorbed and held by theelectrostatic chuck 110.

Further, on the first major surface 11 a side of the ceramic dielectricsubstrate 11, projections 13 are provided as necessary, and a groove 14is provided between the projections 13. The groove 14 is incommunication with the outside, and thus a space is formed between theback surface of the object W placed on the electrostatic chuck 110 andthe groove 14.

The through-hole 15 provided in the ceramic dielectric substrate 11 isconnected to the groove 14. The through-hole 15 is provided to penetratethe ceramic dielectric substrate 11 over a range from the second majorsurface 11 b to the first major surface 11 a of the ceramic dielectricsubstrate 11. The through-holes 15 may be provided at a plurality ofplaces in the ceramic dielectric substrate 11.

In addition, as shown in FIG. 3, the through-hole 15 may have a portionin which an axis of a hole extends in a horizontal direction (theX-direction). The through-hole 15 shown in FIG. 3 has a first holeportion 15 a, a second hole portion 15 b, and a third hole portion 15 c.One end of the first hole portion 15 a is connected to the second majorsurface 11 b of the ceramic dielectric substrate 11. One end of thethird hole portion 15 c is connected to the groove 14. The second holeportion 15 b is connected to the first hole portion 15 a and the thirdhole portion 15 c. More specifically, one end of the second hole portion15 b is connected to the other end of the first hole portion 15 a. Theother end of the second hole portion 15 b is connected to the other endof the third hole portion 15 c. In this manner, the through-hole 15 hasa space physically connecting the first major surface 11 a and thesecond major surface 11 b and is not limited to a straight line-shapedhole. Further, the shape of the through-hole 15 may be, for example, aspherical shape or an arc shape and is not limited to a specific shape.In a case where a plurality of through-holes 15 are provided, if atleast one of the plurality of through-holes 15 satisfies the conditionsof the through-hole of the embodiment, the electrostatic chuck 110according to the embodiment is included in the scope of the invention.

As a material of the ceramic dielectric substrate 11, for example, aCoulomb material is used. The volume resistivity of the Coulomb materialis, for example, about 1×10¹⁴ ohm·centimeter (Ω·cm) or more. In a casewhere the Coulomb material which is used for the ceramic dielectricsubstrate 11 has semipermeability with respect to infrared or visiblelight, it is possible to visually confirm an internal space from thesurface of the ceramic dielectric substrate 11. For this reason, asshown in FIG. 3, in a case where the through-hole 15 has a portion (thesecond hole portion 15 b) in which an axis of a hole extends in thehorizontal direction (the X-direction), it is possible to confirm theposition of the second hole portion 15 b from the surface of the ceramicdielectric substrate 11, and thus it is possible to more easily performprocessing.

By appropriately selecting the height of the projection 13 (the depth ofthe groove 14), the area ratio between the projection 13 and the groove14, the shapes of the projection 13 and the groove 14, or the like, itis possible to control the temperature of the object W or particleswhich are stuck to the object W, to be in a favorable state.

On the other hand, in the base plate 50, a gas introduction path 53 isprovided. The gas introduction path 53 is provided so as to, forexample, penetrate the base plate 50. As shown in FIG. 1, in the gasintroduction path 53, an insulator plug 70 may be provided. The detailsof the insulator plug 70 will be described later. The gas introductionpath 53 may be provided to branch from the middle of another gasintroduction path 53 to the ceramic dielectric substrate 11 side withoutpenetrating the base plate 50. Further, gas introduction paths 53 may beprovided at a plurality of places in the base plate 50.

The gas introduction path 53 communicates with the through-hole 15. Iftransfer gas such as helium (He) is introduced from the gas introductionpath 53 in a state of adsorbing and holding the object W, the transfergas flows into a space provided between the object W and the groove 14,and thus it becomes possible to directly cool the object W by thetransfer gas.

As shown in FIG. 2A, a space 65 is present between the through-hole 15and the gas introduction path 53. More specifically, the space 65 ispresent between an opening 15 d of the through-hole 15 in the secondmajor surface 11 b and the gas introduction path 53. That is, thebonding layer 60 has the space 65. The space 65 is located at a centralportion of the end portion 63 having, for example, a ring shape andextends in the horizontal direction (the X-direction). The space 65 isformed by the ring-shaped end portion 63. A dimension (a distancebetween the end portions 63 (or the end faces 64) facing each other) D1in the X-direction of the space 65 is larger than an opening dimensionD2 of the opening 15 d.

When bonding the ceramic dielectric substrate 11 and the base plate 50together, first, the end portion 63 fabricated in advance is installedon a surface 57 of the base plate 50 or the second major surface 11 b ofthe ceramic dielectric substrate 11 such that the space 65 is presentbetween the through-hole 15 and the gas introduction path 53.Subsequently, an adhesive (for example, a silicone adhesive) whichbecomes the bonding portion 61 after curing is applied while securingthe space 65. Subsequently, the ceramic dielectric substrate 11 and thebase plate 50 are fitted to each other with the end portion 63 and theapplied adhesive interposed therebetween.

After the adhesive is cured (after the bonding layer 60 is formed), athickness (a dimension in the Z-direction) t1 of the bonding layer 60is, for example, about 100 micrometers (μm) or more and 1000 μm or less.More preferably, the thickness t1 of the bonding layer 60 is, forexample, about 200 μm or more and 600 μm or less. In this case, thethickness (the dimension in the Z-direction) of the end portion 63 in astate of being fabricated in advance (a state before installation) is,for example, about 200 μm or more and 600 μm or less. That is, the endportion 63 is crushed in the Z-direction in a process of fitting theceramic dielectric substrate 11 and the base plate 50 to each other.After the adhesive is cured, the thickness of the end portion 63 is thesame as the thickness t1 of the bonding layer 60.

The thickness t1 of the bonding layer 60 is smaller than the dimensionD1 in the X-direction of the space 65. That is, the length in thehorizontal direction (the X-direction) of the space 65 is longer thanthe length in the vertical direction (the Z-direction) of the space 65.In other words, the length in the horizontal direction of the space 65is longer than the thickness t1 of the bonding layer 60. The space 65having a cross-sectional shape which is longer in the horizontaldirection than the vertical direction is connected to the through-hole15 having a cross-sectional shape which is longer in the verticaldirection than the horizontal direction.

The end face 64 of the bonding layer 60 on the space 65 side intersectswith or comes into contact with the second major surface 11 b of theceramic dielectric substrate 11. The area A1 (a first area) in which theend face 64 intersects with the second major surface 11 b is away fromor is recessed from the opening 15 d of the through-hole 15, compared toanother area (a second area) of the end face 64 which is different fromthe area A1.

More specifically, in the area A1 when viewed in a directionperpendicular to a normal to the second major surface 11 b, the anglebetween the second major surface 11 b and the end face 64 becomes largertoward the second major surface 11 b.

Here, in the specification, the “angle between the second major surface11 b and the end face 64” shall refer to the angle between the secondmajor surface 11 b of the ceramic dielectric substrate 11 and a planetangent to an arbitrary point on the end face 64, which is measured on aside of the end portion 63.

As shown in FIG. 2B, for example, an angle A12 between the second majorsurface 11 b and a plane S2 tangent to a point 64 b on the end face 64is larger than an angle A11 between the second major surface 11 b and aplane S1 tangent to a point 64 a on the end face 64.

On the other hand, in an area A2 (a third area) in which the end face 64intersects with or comes into contact with the surface 57 of the baseplate 50, when viewed in a direction perpendicular to a normal to thesecond major surface 11 b, the angle between the second major surface 11b and the end face 64 becomes smaller with distance from the secondmajor surface 11 b in a normal direction. As shown in FIG. 2B, forexample, an angle A14 between the second major surface 11 b and a planeS4 tangent to a point 64 d on the end face 64 is smaller than an angleA13 between the second major surface 11 b and a plane S3 tangent to apoint 64 c on the end face 64.

According to the embodiment, regardless of the durability of theadhesive, it is possible to reduce damage to which the bonding layer 60is subjected. Even if the bonding layer 60 is damaged, it is possible toreduce the scattering of particles.

As shown in FIG. 2A, with respect to the distance d between the end face64 in the area A1 and the center C1 of the through-hole 15 and thedistance D1 between the end portions 63 (the distance between the endfaces 64) facing each other in another area of the end face 64 which isdifferent from the area A1, the following expression is established.

2d≧D1  Expression (1)

In the schematic cross-sectional view shown in FIG. 2A, in a case wherea cross-sectional structure of the end face 64 is asymmetric, thedistance d is set to be a distance of the maximum value among thedistances between the end face 64 in the area A1 and the center C1 ofthe through-hole 15. Due to this, in the area A1, a pocket in whichparticles can be deposited is formed.

The diameter of the through-hole 15 (the opening dimension D2 of theopening 15 d) affects the conductance of the transfer gas flowingthrough the through-hole 15 and a temperature difference in the object Wwhich is adsorbed (a temperature difference between the position on theobject W just above the through-hole 15 and the periphery thereof). Forexample, if the diameter (D2) of the through-hole 15 is small, theconductance is reduced, and thus the flow of the transfer gas sometimesbecomes poor. In contrast, if the diameter (D2) of the through-hole 15is larger, an area in which a temperature difference in the object Wwhich is adsorbed is large (so-called hot spot or cold spot) issometimes generated. According to the knowledge that the inventor(s) hasobtained, it is favorable that the diameter (D2) of the through-hole 15is, for example, 0.04 millimeters (mm) or more and 3 mm or less. It ismore favorable that the diameter (D2) of the through-hole 15 is, forexample, 0.07 mm or more and 2.5 mm or less. It is further favorablethat the diameter (D2) of the through-hole 15 is, for example, 0.1 mm ormore and 2 mm or less.

The longer the distance between plasma and the adhesive (the distancebetween the center C1 of the through-hole 15 and the end face 64), thesmaller the amount of damage to which the adhesive is subjected. On theother hand, as shown in FIG. 4A, the longer the distance d between theend face 64 in the area A1 and the center C1 of the through-hole 15, thelarger the conductance of the transfer gas becomes. Further, if thedistance d is smaller than the diameter (D2) of the through-hole 15, theconductance rapidly deteriorates (becomes small). Accordingly, it isfavorable that the distance d is not less than the minimum value, 0.1mm, of the diameter (D2) of the through-hole 15.

Further, if the distance between the plasma and the adhesive (thedistance between the center C1 of the through-hole 15 and the end face64) is long, due to a difference between the thermal conductivity of theadhesive and the thermal conductivity of a space (air), a temperaturedifference sometimes occurs between the position on the object W justabove the through-hole 15 and the periphery thereof.

As shown in FIG. 4B, in a high-power condition (a heat input conditionof 5000 W to the surface of the electrostatic chuck 110), when thedistance d between the end face 64 in the area A1 and the center C1 ofthe through-hole 15 is 1.85 mm, the temperature difference becomes 5° C.Further, when the distance d between the end face 64 in the area A1 andthe center C1 of the through-hole 15 is 4.0 mm, the temperaturedifference becomes 20° C.

Further, in a low-power condition (a heat input condition of 3000 W tothe surface of the electrostatic chuck 110), when the distance d betweenthe end face 64 in the area A1 and the center C1 of the through-hole 15is 1.85 mm, the temperature difference becomes 3.3° C. When the distanced between the end face 64 in the area A1 and the center C1 of thethrough-hole 15 is 5.0 mm, the temperature difference becomes 20° C.

In a plasma process, an in-plane temperature difference is one of theimportant items. According to the knowledge that the inventor(s) hasobtained, it is favorable that the temperature difference is suppressedto 20° C. or less. For this reason, it is favorable that the distance dis 5.0 mm or less.

Therefore, it is favorable that the distance d between the end face 64in the area A1 and the center C1 of the through-hole 15 is 0.1 mm ormore and 5.0 mm or less. It is favorable that the distance d between theend face 64 in the area A1 and the center C1 of the through-hole 15 is0.2 mm or more and 4.5 mm or less. It is more favorable that thedistance d between the end face 64 in the area A1 and the center C1 ofthe through-hole 15 is 0.4 mm or more and 4 mm or less. It is furtherfavorable that the distance d between the end face 64 in the area A1 andthe center C1 of the through-hole 15 is 0.6 mm or more and 3.7 mm orless.

According to this, it is possible to attain both a reduction in theamount of damage to which the adhesive is subjected and uniformtemperature distribution of the object W.

A material of the end portion 63 may be the same as a material of thebonding portion 61 or may also be different from a material of thebonding portion 61.

In a case where the material of the end portion 63 is the same as thematerial of the bonding portion 61, it is possible to further enhance anadhesive force between the bonding portion and the end portion.

In a case where the material of the end portion 63 is different from thematerial of the bonding portion 61, the end portion 63 is made so as notto contain fillers improving thermal conductivity, and thus it ispossible to reduce occurrence of particles. Further, in a case where thematerial of the end portion 63 is different from the material of thebonding portion 61 and a silicone adhesive is used as the bondingportion 61, a material having more excellent plasma resistance than thesilicone adhesive can be used in the end portion 63.

As for the material having more excellent plasma resistance than thesilicone adhesive, a fluorine-based material can be given as an example.A fluorocarbon-based elastomer having “—CF₂—” as a basic skeleton can begiven as an example. Further, a fluorocarbon-based elastomer in which abasic structure of “—CF₂—CF(CF₃)—O—” is linked to a silicone chain canbe given as an example. Further, a fluorosilicone rubber having“—SiF₂—O—” and “Si(CH₃)₂—O—” as a basic skeleton can be given as anexample. In addition, polyimide, acrylic polymer material, epoxy-basedpolymer material, or the like can be given as an example.

In addition, even in a case where the material of the end portion 63 isthe same as the material of the bonding portion 61, or even in a casewhere the material of the end portion 63 is different from the materialof the bonding portion 61, a boundary line 66 is present between the endportion 63 and the bonding portion 61. Due to this, in relation to thebonding between the ceramic dielectric substrate 11 and the base plate50, it is possible to determine whether or not the bonding layer 60 hasthe end portion 63 fabricated in advance.

The thermal conductivity of the adhesive which is used in the bondingportion 61 is, for example, 0.2 watts/meter·kelvin (W/m·K) or more. Itis more favorable that the thermal conductivity of the adhesive which isused in the bonding portion 61 is 0.4 W/m·K or more. It is furtherfavorable that the thermal conductivity of the adhesive which is used inthe bonding portion 61 is 0.8 W/m·K. The thermal conductivity of theadhesive which is used in the bonding portion 61 is, for example, 4.0W/m·K or less. It is more favorable that the thermal conductivity of theadhesive which is used in the bonding portion 61 is 3.0 W/m·K or less.The dielectric breakdown strength of the adhesive which is used in thebonding portion 61 is, for example, 1 kilovolt/millimeter (kV/mm) ormore. It is more favorable that the dielectric breakdown strength of theadhesive which is used in the bonding portion 61 is 2 kV/mm or more. Itis further favorable that the dielectric breakdown strength of theadhesive which is used in the bonding portion 61 is 5 kV/mm or more. Thedielectric breakdown strength of the adhesive which is used in thebonding portion 61 is, for example, 50 kV/mm or less. A heat resistancetemperature of the adhesive which is used in the bonding portion 61 is60° C. or more.

According to this, it is possible to use an adhesive which can maintaininsulation while maintaining good heat transfer even if theelectrostatic chuck 110 is used in a high-temperature process. Further,it is possible to have elasticity capable of alleviating a differencebetween the thermal expansion of the ceramic dielectric substrate 11 andthe thermal expansion of the base plate 50. As a result, the life of theelectrostatic chuck 110 is lengthened.

As shown in FIG. 2A, the distance d between the end face 64 in the areaA1 and the center C1 of the through-hole 15 is larger than a radius((D4)/2) of an opening 15 e on the first major surface 11 a side. Due tothis, regardless of the durability of the adhesive, it is possible toreduce damage to which the bonding layer 60 is subjected. Even if thebonding layer 60 is damaged, it is possible to reduce the scattering ofparticles.

As shown in FIGS. 2A and 2B, the end portion 63 comes into contact withthe second major surface 11 b of the ceramic dielectric substrate 11 ina plane 63 b rather than a point and comes into contact with the surface57 of the base plate 50 in a plane 63 c rather than a point. In theschematic cross-sectional view shown in FIG. 2A, a length (the length inthe X-direction of the plane 63 b) D5 of a portion in which the endportion 63 comes into contact with the second major surface 11 b of theceramic dielectric substrate 11 is longer than the thickness t1 of thebonding layer 60. In the schematic cross-sectional view shown in FIG.2A, a length (the length in the X-direction of the plane 63 c) D6 of aportion in which the end portion 63 comes into contact with the surface57 of the base plate 50 is longer than the thickness t1 of the bondinglayer 60. Each of the length D5 and the length D6 is, for example, about500 μm or more.

According to this, since the end portion 63 is in contact with each ofthe second major surface 11 b and the surface 57 in a plane rather thana point, it is possible to prevent occurrence of a space in the bondinglayer 60. That is, an outer peripheral portion which is an outerperipheral portion of the end portion 63 and is on the side opposite tothe space 65 when viewed from the end portion 63 is filled with a resinmaterial.

As described above, the end portion 63 is crushed in the Z-direction inthe process of fitting the ceramic dielectric substrate 11 and the baseplate 50 to each other. The plane 63 b in which the end portion 63 iscrushed by the ceramic dielectric substrate 11 is on the same plane as abonded surface (the second major surface 11 b) of the ceramic dielectricsubstrate 11. The plane 63 c in which the end portion 63 is crushed bythe base plate 50 is on the same plane as a bonded surface (the surface57) of the base plate 50.

FIG. 5 is a schematic enlarged view showing the vicinity of anotherbonding layer of the embodiment.

FIG. 5 is a schematic enlarged view of a portion equivalent to theportion A shown in FIG. 1.

A bonding layer 60 a shown in FIG. 5 has the bonding portion 61 and anend portion 63 a. The end portion 63 a has, for example, a ring-likeshape. The end face 64 of the bonding layer 60 a on the space 65 sideintersects with or comes into contact with the second major surface 11 bof the ceramic dielectric substrate 11. An area A3 (the first area) inwhich the end face 64 intersects with the second major surface 11 b isaway from or is recessed from the opening 15 d of the through-hole 15,compared to another area (the second area) of the end face 64 which isdifferent from the area A3.

In the bonding layer 60 a shown in FIG. 5, a distance D3 between the endportions 63 (or the end faces 64) facing each other becomes shorter withdistance from the second major surface 11 b in the normal direction.That is, the end face 64 has an inclination by which the distance D3between the end portions 63 (or the end faces 64) facing each otherbecomes shorter with distance from the second major surface 11 b in thenormal direction. In addition, other structures or a material of eachmember is as described above with respect to FIGS. 1 to 3.

According to the example shown in FIG. 5, regardless of the durabilityof the adhesive, it is possible to reduce damage to which the bondinglayer 60 a is subjected. Even if the bonding layer 60 a is damaged, itis possible to reduce the scattering of particles.

FIG. 6 is a schematic enlarged view showing the vicinity of stillanother bonding layer of the embodiment.

The electrostatic chuck 110 according to the embodiment may be providedwith the insulator plug 70.

The insulator plug 70 may be provided in the gas introduction path 53provided in the base plate 50. The insulator plug 70 is fitted into theceramic dielectric substrate 11 side of the gas introduction path 53. Asshown in FIG. 6, for example, on the ceramic dielectric substrate 11side of the gas introduction path 53, a counterbore portion 53 a isprovided. The counterbore portion 53 a is provided in a tubular shape.Due to appropriately designing the inner diameter of the counterboreportion 53 a, the insulator plug 70 may be fitted into the counterboreportion 53 a.

The insulator plug 70 has a ceramic porous body 71. The ceramic porousbody 71 is provided in a tubular shape (for example, a cylindricalshape) and fitted to the counterbore portion 53 a. The shape of theinsulator plug 70 is preferably a cylindrical shape. However it is notlimited to a cylindrical shape. For the ceramic porous body 71, amaterial having insulation properties is used. As a material of theceramic porous body 71, for example, Al₂O₃, Y₂O₃, ZrO₂, MgO, SiC, AlN,Si₃N₄, or glass such as SiO₂ is acceptable. Alternatively, the materialof the ceramic porous body 71 may be Al₂O₃—TiO₂, Al₂O₃—MgO, Al₂O₃—SiO₂,Al₆O₁₃Si₂, YAG, ZrSiO₄, or the like.

The porosity of the ceramic porous body 71 is, for example, 30 percent(%) or more and 60% or less. The density of the ceramic porous body 71is, for example, 1.5 grams/cubic centimeter (g/cm³) or more and 3.0g/cm³ or less. Due to such porosity, the transfer gas such as He flowingthrough the gas introduction path 53 passes through a large number ofpores of the ceramic porous body 71 and is sent from the through-hole 15provided in the ceramic dielectric substrate 11 to the groove 14.

As shown in FIG. 6, with respect to the distance d between the end face64 in the area A1 and the center C1 of the through-hole 15 and a radiusR of the ceramic porous body 71, the following expression isestablished.

d>R  Expression (2)

In addition, other structures or a material of each member is asdescribed above with respect to FIGS. 1 to 3.

Due to this, like an arrow A21, an arrow A22, an arrow A23, and an arrowA24 shown in FIG. 6, the convection of the transfer gas can be createdin the space 65 such that particles are easily deposited in a pocketformed in the area A1. That is, the convection of the transfer gas whichselectively deposits particles in the pocket formed in the area A1 canbe controlled in the space 65. For this reason, even if particles aregenerated, it is possible to reduce the scattering of the particles.Further, the ceramic porous body 71 is provided, whereby it is possibleto have high voltage resistance in the through-hole 15 and the gasintroduction path 53.

FIG. 7 is a schematic enlarged view showing the vicinity of stillanother bonding layer of the embodiment.

The electrostatic chuck 110 shown in FIG. 7 is provided with theinsulator plug 70, similar to the electrostatic chuck 110 describedabove with respect to FIG. 6. The insulator plug 70 is provided in thethrough-hole 15 provided in the ceramic dielectric substrate 11. Theinsulator plug 70 is fitted into the base plate 50 side of thethrough-hole 15. As shown in FIG. 7, for example, the through-hole 15has a counterbore portion 15 f on the base plate 50 side. Thecounterbore portion 15 f forms the opening 15 d of the through-hole 15.The counterbore portion 15 f is provided in a tubular shape. Due toappropriately designing the inner diameter of the counterbore portion 15f, the insulator plug 70 may be fitted into the counterbore portion 15f.

The insulator plug 70 is as described above with respect to FIG. 6. Thatis, the insulator plug 70 has the ceramic porous body 71. The transfergas such as helium passes through the gas introduction path 53 and thespace 65 and passes through the through-hole 15 via the insulator plug70, thereby flowing into the space provided between the object W and thegroove 14. In this manner, in the specification, in the range of the“through-hole”, a hole in which a thing having a pathway through whichgas flows, like, for example, a porous body or the like, is provided inthe middle and through which arbitrary gas or fluid penetrates isincluded.

FIG. 8 is a schematic enlarged view showing the vicinity of stillanother bonding layer of the embodiment.

The electrostatic chuck 110 shown in FIG. 8 is further provided with aheater 91, compared to the electrostatic chuck 110 described above withrespect to FIG. 7. The heater 91 is provided between the base plate 50and the ceramic dielectric substrate 11. The heater 91 is supplied withvoltage, and thus an electric current flows therethrough, whereby theheater 91 generates heat, thereby raising or maintaining the temperatureof the object W.

The heater 91 is fixed to the second major surface 11 b of the ceramicdielectric substrate 11 via the bonding layer 60. Further, the heater 91is fixed to the surface 57 of the base plate 50 via the bonding layer60. That is, the bonding layer 60 is provided between the heater 91 andthe ceramic dielectric substrate 11 and between the heater 91 and thebase plate 50. The bonding layer 60 provided between the ceramicdielectric substrate 11 and the heater 91 has the end portion 63. Theend portion 63 is as described above with respect to FIGS. 1 to 4B. Thebonding layer 60 provided between the base plate 50 and the heater 91may have the end portion 63 or may not have the end portion 63.

As shown in FIG. 8, the heater 91 is provided away from the gasintroduction path 53. The bonding layer 60 provided between the baseplate 50 and the heater 91 is provided away from the gas introductionpath 53. The end portion 63 of the bonding layer 60 provided between theceramic dielectric substrate 11 and the heater 91 is provided on theside opposite to the gas introduction path 53 when viewed from an endportion of the heater 91. That is, a shortest distance D8 between thebonding layer 60 provided between the ceramic dielectric substrate 11and the heater 91 and a center C2 of the gas introduction path 53 islonger than a shortest distance D7 between the heater 91 and the centerC2 of the gas introduction path 53. As described above with respect toFIG. 2A, the space 65 having a cross-sectional shape which is longer inthe horizontal direction than the vertical direction is connected to thethrough-hole 15 having a cross-sectional shape which is longer in thevertical direction than the horizontal direction.

FIG. 9 is a schematic enlarged view showing the vicinity of stillanother bonding layer of the embodiment.

The electrostatic chuck 110 shown in FIG. 9 is provided with the heater91, similar to the electrostatic chuck 110 described above with respectto FIG. 8. The bonding layer 60 provided between the ceramic dielectricsubstrate 11 and the heater 91 has the end portion 63. The end portion63 is as described above with respect to FIGS. 1 to 4B. The bondinglayer 60 provided between the base plate 50 and the heater 91 may havethe end portion 63 or may not have the end portion 63.

As shown in FIG. 9, the end portion of the heater 91 is provided onapproximately the same plane as the inner surface of the gasintroduction path 53. An end portion of the bonding layer 60 providedbetween the base plate 50 and the heater 91 is provided on approximatelythe same plane as the inner surface of the gas introduction path 53.

According to the electrostatic chucks 110 shown in FIGS. 7 to 9,regardless of the durability of the adhesive, it is possible to reducedamage to which the bonding layer 60 is subjected. Even if the bondinglayer 60 is damaged, it is possible to reduce the scattering ofparticles. Further, the ceramic porous body 71 is provided, whereby itis possible to have high voltage resistance in the through-hole 15 andthe gas introduction path 53.

FIG. 10 is a schematic enlarged view showing the vicinity of stillanother bonding layer of the embodiment.

FIG. 11 is a schematic enlarged view showing the vicinity of stillanother bonding layer of the embodiment.

In the electrostatic chucks 110 shown in FIGS. 10 and 11, the bondinglayer 60 is provided as a sheet. That is, the bonding layer 60 exhibitsa sheet shape. For this reason, the bonding layer 60 does not have, forexample, the ring-like end portion 63 as described above with respect toFIGS. 1 to 9. The sheet shape exhibits a state where the bonding portion61 bonding the second major surface 11 b and the base plate 50 togetherand the end portion 63 forming the space 65 are integrated with eachother with the same material.

The end face 64 of the bonding layer 60 shown in FIG. 10 has the sameshape as the shape of the end face 64 of the bonding layer 60 describedabove with respect to FIGS. 2A and 2B.

The end face 64 of the bonding layer 60 shown in FIG. 11 has the sameshape as the shape of the end face 64 of the bonding layer 60 describedabove with respect to FIG. 5.

According to the electrostatic chucks 110 shown in FIGS. 10 and 11, evenin a case where the bonding layer 60 is provided as a sheet, regardlessof the durability of the adhesive, it is possible to reduce damage towhich the bonding layer 60 is subjected. Even if the bonding layer 60 isdamaged, it is possible to reduce the scattering of particles.

Next, a simulation of the end portion 63 of the bonding layer 60 carriedout by the inventor(s) will be described with reference to the drawings.

FIG. 12 is a schematic cross-sectional view showing the conditions ofthe simulation.

FIGS. 13A to 13C are schematic perspective views illustrating an exampleof the results of the simulation.

FIGS. 14A and 14B are schematic perspective views illustrating anexample of the results of the simulation.

FIG. 13A is a schematic view showing the cross-sectional shape of theend portion 63 of the bonding layer 60 before it is compressed in abonding process. FIGS. 13B, 13C, 14A and 14B are schematic views showingthe cross-sectional shape of the end portion 63 of the bonding layer 60after it is compressed in the bonding process.

As shown in FIG. 12, in the simulation, the end portion 63 is sandwichedbetween a first fixing portion 97 and a second fixing portion 98. Thefirst fixing portion 97 is equivalent to, for example, the base plate50. The second fixing portion 98 is equivalent to, for example, theceramic dielectric substrate 11.

As the end portion 63 of the bonding layer 60, a model having aring-like shape was made. An outer diameter D11 of the end portion 63before compression is 3 mm or more and 10 mm or less. An inner diameterD12 of the end portion 63 before compression is 1 mm or more and 5 mm orless. In the simulation, the Young's modulus of a material of the endportion 63 was set to be 0.1 megapascals (MPa) or more and 20 MPa orless. Further, the Poisson's ratio of the material of the end portion 63was set to be 0.3 or more and 0.5 or less.

In the simulation, compressive stress was applied to the end portion 63by moving the second fixing portion 98 toward the first fixing portion97, like an arrow A25 shown in FIG. 12. The results of the simulationare as shown in FIGS. 13A to 14B.

That is, FIG. 13B shows the displacement in a radial direction of theend portion 63 when a thickness D13 of the end portion 63 is thickerthan the thickness t1 of the bonding layer 60 after bonding. FIG. 13Cshows the displacement in the radial direction of the end portion 63when the end portion 63 has been compressed to the thickness t1 of thebonding layer 60 after bonding. FIG. 14A shows the displacement in theradial direction of the end portion 63 when the thickness D13 of the endportion 63 is thicker than the thickness t1 of the bonding layer 60after bonding. FIG. 14B shows the displacement in a thickness direction(the Z-direction) of the end portion 63 when the end portion 63 has beencompressed to the thickness t1 of the bonding layer 60 after bonding. InFIGS. 13A to 14B, the magnitude of the displacement is shown by a colorof shading.

As shown in FIG. 14B, a circle 93 having a diameter of the same lengthas the thickness D13 of the end portion 63 after compression isconsidered. In this case, the curvature of the end face 64 in an area A4(the first area) in which the end face 64 of the end portion 63intersects with the second fixing portion 98 is larger than thecurvature of the circle 93. On the other hand, the curvature of the endface 64 in another area A5 (the second area) of the end face 64 which isdifferent from the area A4 is smaller than the curvature of the circle93. That is, the curvature of the end face 64 in the area A4 (the firstarea) in which the end face 64 of the end portion 63 intersects with thesecond fixing portion 98 is larger than the curvature of the end face 64in another area A5 (the second area) of the end face 64 which isdifferent from the area A4.

The area A4 is equivalent to the area A1 described above with respect toFIG. 2A. The other area A5 of the end face 64 which is different fromthe area A4 is equivalent to another area of the end face 64 which isthe area described above with respect to FIG. 2A and is different fromthe area A1, and is, for example, an intermediate area between the firstfixing portion 97 and the second fixing portion 98.

The curvature of an end face 67 on the outside of the end portion 63 islarger than the curvature of the end face 64 on the inside of the endportion 63. The visible outline of the end face 67 on the outside of theend portion 63 is equivalent to the boundary line 66 (refer to FIG. 2A)between the end portion 63 and the bonding portion 61.

The embodiments of the invention have been described above. However, theinvention is not limited to the above description. Those skilled in theart can appropriately modify the above embodiments, and suchmodifications are also encompassed within the scope of the invention aslong as they include the features of the invention. For instance, theshape, dimension, material, arrangement and the like of variouscomponents in the electrostatic chucks 110, and the installationconfiguration and the like of the bonding portion 61 and the end portion63 are not limited to those illustrated, but can be modifiedappropriately. Furthermore, the configuration using Coulomb force isillustrated as the electrostatic chucks 110. However, the configurationusing Johnson-Rahbek force may be applicable as the electrostatics 110.

Furthermore, various components in the above embodiments can be combinedwith each other as long as technically feasible. Such combinations arealso encompassed within the scope of the invention as long as theyinclude the features of the invention.

What is claimed is:
 1. An electrostatic chuck comprising: a ceramicdielectric substrate having a first major surface on which an object tobe adsorbed is placed, a second major surface on an opposite side to thefirst major surface, and a through-hole provided over from the secondmajor surface to the first major surface; a metallic base plate whichsupports the ceramic dielectric substrate and has a gas introductionpath that communicates with the through-hole; and a bonding layer whichis provided between the ceramic dielectric substrate and the base plateand includes a resin material, the bonding layer having a space which isprovided between an opening of the through-hole in the second majorsurface and the gas introduction path and is larger than the opening ina horizontal direction, and a first area in which an end face of thebonding layer on a side of the space intersects with the second majorsurface being recessed from the opening further than another second areaof the end face which is different from the first area.
 2. The chuckaccording to claim 1, wherein in the first area when viewed in adirection perpendicular to a normal to the second major surface, anangle between the second major surface and the end face becomes largertoward the second major surface.
 3. The chuck according to claim 2,wherein a third area in which an angle between the second major surfaceand the end face becomes smaller with distance from the second majorsurface in a direction of the normal is provided.
 4. The chuck accordingto claim 1, wherein a distance between the end faces facing each otherbecomes shorter with distance from the second major surface in adirection of the normal.
 5. The chuck according to claim 1, wherein in adistance d between the end face in the first area and a center of thethrough-hole and a distance D between the end faces facing each other inthe second area, a relational expression of 2d≧D is established.
 6. Thechuck according to claim 5, wherein the distance d is 0.1 millimeters ormore and 5.0 millimeters or less.
 7. The chuck according to claim 1,wherein the bonding layer has a bonding portion which bonds the secondmajor surface and the base plate together, and an end portion which hasthe end face and forms the space, and a material of the bonding portionis different from a material of the end portion.
 8. The chuck accordingto claim 1, wherein the bonding layer has a bonding portion which bondsthe second major surface and the base plate together, and an end portionwhich has the end face and forms the space, and a material of thebonding portion is the same as a material of the end portion.
 9. Thechuck according to claim 7, wherein thermal conductivity of an adhesivewhich is used in the bonding portion is 0.1 watts/meter·kelvin or more,dielectric breakdown strength of an adhesive which is used in thebonding portion is 1 kilovolt/millimeter or more, and a heat resistancetemperature of an adhesive which is used in the bonding portion is 40°C. or more.
 10. The chuck according to claim 5, further comprising: aporous body provided in the gas introduction path, wherein in thedistance d and a radius R of the porous body, a relational expression ofd>R is established.
 11. The chuck according to claim 5, wherein thedistance d is larger than a radius of an opening of the through-hole ona side of the first major surface.
 12. The chuck according to claim 1,wherein a length in the horizontal direction of the space is longer thana thickness of the bonding layer.
 13. The chuck according to claim 7,wherein the end portion comes into contact with each of the second majorsurface and the base plate in a plane, and a length in the horizontaldirection of the plane in which the end portion comes into contact witheach of the second major surface and the base plate is longer than athickness of the bonding layer.
 14. The chuck according to claim 13,wherein an outer peripheral portion of the end portion, the outerperipheral portion being on an opposite side to the space when viewedfrom the end portion, is filled with the resin material.
 15. The chuckaccording to claim 13, wherein a plane in which the second major surfacecomes into contact with the end portion is on a same plane as a plane inwhich the second major surface is bonded by the bonding layer, and aplane in which the base plate comes into contact with the end portion ison a same plane as a plane in which the base plate is bonded by thebonding layer.
 16. The chuck according to claim 13, wherein curvature ofthe end face in the first area is larger than curvature of the end facein the second area.
 17. The chuck according to claim 1, wherein theceramic dielectric substrate includes a Coulomb material having volumeresistivity of 1×10¹⁴ ohm·centimeter or more.